1. Field of the Invention
The present invention relates to an adaptive recording method and apparatus for a highdensity optical recording apparatus, and more particularly, to an adaptive recording method and apparatus for optimizing power of a laser diode.
2. Description of the Related Art
High-capacity recording media are required in a multimedia age and optical recording apparatuses using the same include magnetic optical disc driver (MODD), digital versatile disc random access memory (DVD-RAM) driver and the like.
These optical recording apparatuses require an optimal system state and precision as the recording density increases. In general, if the recording capacity increases, jitter of an overwrite pulse for a radial tilt increases in a direction of a time axis. Thus, it is very important to minimize the jitter for attaining high-density recording.
FIG. 1 is a block diagram of a conventional optical recording apparatus.
First, a recording waveforn controller 120 controls recording waveforms in accordance with input NRZI data. An overwrite pulse generator 140 generates overwrite pulses in accordance with an control output generated from the recording waveform controller 120. A laser diode driver 150 drives a laser diode 152 in accordance with levels of the overwrite pulses generated from the overwrite pulse generator 140. Also, a gain adjuster 158 adjusts a gain of an optical signal input from a disc 154 through a photodiode (PD) 156. A comparator 160 compares the voltage of a signal output from the gain adjuster 158 with a reference voltage. A counter 170 up/down counts in accordance with the result of the comparator 160. A digital-analog converter (DAC) 180 converts up/down counted values into analog values and applies the converted values to the laser diode driver 150.
FIGS. 2A through 2E are waveform diagrams of overwrite pulses generated from the overwrite pulse generator 140 shown in FIG. 1.
Overwrite pulses of input NRZI (Non Return to Zero Inversion) data having recorded mark sizes of 3T, 5T and 11T, as shown in FIG. 2A, are formed in a state specified in a format book, as shown in FIG. 2E, and then recorded. Here, the NRZI data are divided into marks and spaces. During a period of the spaces, the laser diode is in an erase power state to thus erase existing data. Recorded marks of NRZI data composed of 3T, 4T, . . . , 14T, in which the interval of each T is 1L, are recorded by changing only the size of multi-pulses without changing the numbers of the first pulse, the last pulse and the cooling pulse.
In other words, the waveforms of the overwrite pulse shown in FIG. 2E are formed by the combination of read power (FIG. 2B), peak power, which is also called write power, (FIG. 2C), and bias power, which is also called erase power (FIG. 2D).
The waveform of the overwrite pulses is the same as those of the first generation DVD-RAM standard of 2.6 giga bytes (GB). In other words, according to the 2.6 GB DVD-RAM standard, the waveform of an overwrite pulses consists of the first pulse, multi-pulse chains and the last pulse. The rising edge of the first pulse of the basic overwrite pulses is delayed by T/2 from the rising edge of a recorded mark. The rising edge of the first pulse can be shifted back and forth in units of 1 nano second (ns). The last pulse can also be shifted back and forth in units of 1 ns. The multi-pulse chains are divided into several short pulses to reduce thermal accumulation in the rear portion of the recorded mark, thereby suppressing deformation of recorded marks.
In the structure of such an overwrite pulse, the waveform of overwrite pulses is formed, irrespective of the preceding and following spaces.
Therefore, when forming and recording overwrite pulses formed into a constant power level, as shown in FIG. 2E, jitter may be caused in accordance with input NRZI data, because recorded marks have thermal accumulation occurring in the front or rear portions thereof, or the domain sizes formed depending on the sizes of preceding and following spaces are not constant. This may significantly degrade overall system performance. Also, this makes it difficult to use high-density DVD-RAM, for example, the second generation DVD-RAM of 4.7 GB.
To solve the above problems, it is an object of the present invention to provide a method for adaptively forming overwrite pulses in accordance with marks or spaces of input NRZI data in a high-density optical recording apparatus.
It is another object of the present invention to provide an apparatus for adaptively forming overwrite pulses in accordance with marks or spaces of input NRZI data in a high-density optical recording apparatus.
To achieve the first object, there is provided an adaptive recording method in a method for optimizing read power, peak power and write power for overwrite pulses and supplying the same to a laser diode, the adaptive recording method comprising the steps of (a) discriminating the mark size of input NRZI data, and (b) varying power of the overwrite pulse in accordance with the discriminated mark size. In step (b), power levels of the laser diode are varied based on levels of the write power controlled an automatic laser power control (ALPC).
According to another aspect of the present invention, there is provided an adaptive recording apparatus in an apparatus for controlling power of a laser diode, the adaptive recording apparatus comprising a discriminator for discriminating the mark size of input data or relationship between preceding and following spaces and outputting different power levels accordingly, a generator for controlling the waveform of overwrite pulses in accordance with the input data to generate overwrite pulses, and a laser diode driver for converting differentiated value between the value of the power level output from the discriminator and a reflected optical signal level into a current signal, and adaptively driving the laser diode in accordance with the mark size.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.